We have produced amplitude-modulated near-ultraviolet light, centered at 390 nm, using an inexpensive, commercially available blue light emitting diode (LED). The fluorescence lifetimes of standard fluorophores were measured in the frequency -domain using the phase modulation technique, producing fluorescence lifetimes that agree with those reported in the literature. The ability to modulate the LED at high frequencies, along with the UV output, allows its use as an inexpensive UV light source in the fluorescence lifetime optical sensors and even frequency-domain fluorometers.[unreadable]